In the fence scene, when the three are climbing the fence in order to get to the other side -

why are they climbing the fence in the first place - it is obvious that they can just go through it (as long as the power is out of course) because the gap between the wires is sufficant for a person (especially the kids, but the doctor as well) to go through...

I'm a little hazy on the movie, but if I recall, the doctor went up to the fence and tried to stick his head through the openings (as well as pull them far enough apart to allow an individual to pass through), and was clearly unable to do this. This was just after he made the joke that the fence was "shocking" him. This is the reason they decided to "climb" as opposed to go "through."
What does everyone else think?

Doctor Grant tries to pull the wires apart but the gap is still too small, yet when the shot comes out, away from the fence as the children begin to climb, the gaps appear large enough for at least the children to squeeze through.